三嗪框架聚合物膜用于有机纳滤甲醇/正己烷分离

doi:10.11949/0438-1157.20230091

摘要/Abstract

摘要：

具备耐各种有机溶剂的微孔聚合物膜在有机纳滤领域逐渐受到重视。采用双氰基单体的超酸催化成环聚合反应，制备微孔框架聚合物薄膜(CTF-BP)，该膜具备良好的力学性能，可耐受甲醇和正己烷等常见有机溶剂。CTF-BP膜内大量<1.0 nm的微孔通道使膜具备良好的筛分性能，其截留分子量为550。膜内含有的三嗪结构与羟基具有较强的亲和性，使甲醇的跨膜通量［1.10 L/(m²·h·bar)］显著高于黏度更低的正己烷通量［0.23 L/(m²·h·bar)］。采用纳滤操作将膜用于分离含低浓度甲醇的正己烷溶液［含5%(质量)甲醇的正己烷溶液］，结果显示甲醇/正己烷分离因子最高可达到1485，渗透液的总流量超过3.21 kg/(m²·h)。证实CTF-BP膜有望实现高效甲醇/正己烷分离。

关键词: 三嗪框架, 聚合物膜, 耐有机溶剂, 纳滤, 甲醇/正己烷分离

Abstract:

Microporous polymer membranes resistant to various organic solvents have gradually attracted attention in the field of organic nanofiltration. Herein, we report a covalent triazine framework membrane (CTF-BP) synthesized by a super acid-catalyzed organo-sol-gel reaction of commercially available aromatic nitrile monomer. This membrane exhibits good mechanical strength and is dimensionally stable in organic solvents, such as methanol, n-hexane, etc. Size sieving by the robust micropores (<1.0 nm) confers the membrane with a cut-off molecular weight as low as 550. The hydrogen interaction between triazine rings and the hydroxyl groups facilitates the transport of methanol, the flux of which reaches up to 1.10 L/(m²·h·bar), a value much higher than that of the less viscous n-hexane [0.23 L/(m²·h·bar)]. To demonstrate the practical applicability, this membrane is utilized to separate n-hexane containing low concentration of methanol solution [5% (mass) methanol], and a maximum separation factor of 1485 and a methanol flux of 3.21 kg/(m²·h) are obtained. These results demonstrate the great potential of the CTF-BP membranes in the recovery of methanol from its mixture with n-hexane via organic solvent nanofiltration (OSN).

Key words: covalent triazine framework, polymer membrane, organic solvent resistant, nanofiltration, methanol/ n-hexane separation

中图分类号:

TQ 028.8

吕阳光, 左培培, 杨正金, 徐铜文. 三嗪框架聚合物膜用于有机纳滤甲醇/正己烷分离[J]. 化工学报, 2023, 74(4): 1598-1606.

Yangguang LYU, Peipei ZUO, Zhengjin YANG, Tongwen XU. Triazine framework polymer membranes for methanol/n-hexane separation via organic solvent nanofiltration[J]. CIESC Journal, 2023, 74(4): 1598-1606.

图/表 7

图1 4,4'-联苯甲腈的超酸催化聚合制备微孔三嗪框架聚合物（a）及膜制备过程（b）

Fig.1 Covalent triazine framework synthesized by the superacid catalytic polymerization of 4,4′-biphenyldicarbonitrile (a) and schematic diagram of the preparation of CTF-BP membranes (b)

图2 错流过滤装置示意图

Fig.2 Schematic of the cross-flow permeation apparatus

图3 CTF-BP膜傅里叶红外光谱（a）和固态核磁碳谱图（b）

Fig.3 Fourier transform infrared spectra (a) and 13C solid-state NMR spectrum (b) of CTF-BP membrane

图4 以HPAN（a）和载玻片（b）为基底的CTF-BP膜断面SEM图；CTF-BP的表面SEM图（c）；CTF-BP膜的表面AFM图（d）；CTF-BP膜附着在铁圈上（e）和HPAN基底上（f）实物图

Fig.4 Cross-sectional SEM images of the CTF-BP membrane supported on porous HPAN (a) and glass plate (b)， SEM (c) and AFM (d) images of the surface morphology of CTF-BP， photos of a free-standing CTF-BP membrane on an iron loop (e) and on an HPAN substrate (f)

图5 CTF-BP等温CO2吸脱附曲线（273 K）（a）;基于CO2等温吸附曲线，采用密度泛函理论模拟计算得到的CTF-BP的孔径分布（b）

Fig.5 CO2 sorption isotherms of CTF-BP membrane (273 K) (a), the pore size distribution of CTF-BP calculated according to density functional theory (DFT) based on the CO2 sorption isotherms (b)

图6 CTF-BP膜对单个染料分子的截留率和对应的分子量(a)；偶氮苯、甲基红、酸性品红混合物溶液跨膜渗透前后的紫外吸收波谱（b）；酸性品红溶液跨膜渗透前后的紫外吸收波谱（c）；长时间测试下酸性品红的截留率和渗透液通量（20 mg/L）（d）

Fig.6 Rejection rate as a function of the molecular weight of varied dyes (a), the UV-Vis spectra of the feed mixture consisting of AB, MR, AF and permeant (b), ultraviolet visible absorption spectra of AF before and after filtration through CTF-BP membranes (c), long-term OSN test of CTF-BP membrane in separating a solution mixture of acid fuchsine and methanol (20 mg/L) (d)

图7 溶剂通过CTF-BP膜的渗透通量和溶剂黏度关系（a）；甲醇、乙醇、正己烷通过CTF-BP膜的渗透通量随时间的变化曲线（b）；CTF-BP膜分离甲醇/正己烷混合溶液机理示意图及在100 μl甲醇中加入0.05、0.10、0.15、0.20 g 1,3,5-三嗪核磁滴定结果（c）;进料液为不同浓度的甲醇/正己烷混合溶液时渗透液的总流量以及其中甲醇含量（d）；进料液为8%(质量)甲醇/正己烷混合溶液时跨膜渗透液的总流量和其中甲醇含量随时间的变化（e）

Fig.7 Solvents permeance through the CTF-BP membrane versus the solvent viscosity for the membrane (a)， plot of methanol, ethanol and n-hexane permeances with time for CTF-BP membranes (b), schematic diagram of the separation mechanism of methanol/n-hexane mixture (the upper panel) and 1H NMR spectra of 100 μl methanol with varied mass of 1,3,5-triazine from 0.05 g to 0.20 g (c), dependence of methanol concentration in permeate and total flux on methanol concentration in feed for membranes of methanol/n-hexane mixture (d), long time separation performance of methanol/n-hexane with the 8% (mass) methanol in feed solution (e)

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